conceptual q's
right hand rule
solenoids
misc
100
For calculating magnetic fields, what are the advantages and disadvantages of the Biot-Savart law?
What is it works with any magnetic field produced by a current loop. The disadvantage is that it can take a long time.
100
A negatively charged particle, q, is moving in a uniform magnetic field traveling in a circle of radius R, as shown. What is the direction of B?
out of page
100
What is this equation for? And what does each variable mean?
B =μ0I(N/L)
solenoid
100
What is the magnetic field strength of a point 10 cm to the right of a 10 Coulomb positively charged rod resting in the plane of the page?
B= 0 T
Solution: Magnetic fields are generated by moving electric charges, this is a rod staying still with some charge, not with a current (which by definition a current is moving charges)
200
A magnetic field exerts a force on the moving electrons in a current carrying wire. What exerts the force on a wire?
A force on a wire is exerted by an external magnetic field created by a wire or another magnet.
200
True or false: Uniform magnetic fields are generated by wires carrying constant currents.
False:The relation between magnetic field strength and distance from a current carrying wire? B= 0I2r, so wires carrying constant current are dependent on distance as in the equation. Constant B-fields are only created by solenoids from what we have discussed in class so far.
200
Why does increasing the number of turns per unit length increase B field strength in the center?
Doing so increases the superposition of the B field from the current rings in the same amount of length.
200
How many electrons flow through a point in a wire in 3.00 s if there is a constant current of 𝐼=4.00A?
7.5 x 10^19 electrons
use I=dQ/dt
300
Considering the magnetic force law, are the velocity and magnetic field always perpendicular? Are the force and velocity always perpendicular? What about the force and magnetic field?
Velocity and magnetic field can be set together in any direction. If there is a force, the velocity is perpendicular to it. The magnetic field is also perpendicular to the force if it exists.
300
what is ampere's law for each figure?
a) u(2A)
b) u(9A)
c) 0
d) u(2A)
e) u(5A)
300
Which of the following adjustments increases the magnetic field at the center of a solenoid?
Increase solenoid length
Increase current flow through the solenoid
Decrease the number of turns per length of the wire
2
Solution:
So only II (increasing current will increase mag. Field
300
Two long wires, one of which has a semicircular bend of radius R, are positioned as shown in the accompanying figure. If both wires carry a current I, how far apart must their parallel sections be so that the net magnetic field at P is zero? Does the current in the straight wire flow up or down?
𝑎=2𝑅/𝜋 the current in the wire to the right must flow up the page.
400
Is Ampère’s law valid for all closed paths? Why isn’t it normally useful for calculating a magnetic field?
Ampère’s law is valid for all closed paths, but it is not useful for calculating fields when the magnetic field produced lacks symmetry that can be exploited by a suitable choice of path.
400
D because:
Is true based on Right Hand Rule
For centripetal motion, the tangential velocity stays constant despite different radius. (All forces are perpendicular to the displacement so W=0 so delta KE =
F = mv2r (centripetal acceleration is v2/r) Both F and v are constant, hence if r is bigger, then mass is bigger too.
400
A solenoid is wound with 2000 turns per meter. When the current is 5.2 A, what is the magnetic field within the solenoid?
1.3 e-2 T
400
What is the strength of the electric field in a region where the electric potential is constant?
The electric field strength is zero because electric potential differences are directly related to the field strength. If the potential difference is zero, then the field strength must also be zero.
500
If you cut a bar magnet into two pieces, will you end up with one magnet with an isolated north pole and another magnet with an isolated south pole? Explain your answer.
The bar magnet will then become two magnets, each with their own north and south poles. There are no magnetic monopoles or single pole magnets.
500
Answer: C
500
A toroid with a square cross section 3.0 cm × 3.0 cm has an inner radius of 25.0 cm. It is wound with 500 turns of wire, and it carries a current of 2.0 A. What is the strength of the magnetic field at the center of the square cross section?
0.0008 T
500
A charge q is placed at one of the corners of a cube of side a, as shown below. Find the magnitude of the electric flux through the shaded face due to q. Assume 𝑞>0q>0.
Make a cube with q at the center, using the cube of side a. This would take four cubes of side a to make one side of the large cube. The shaded side of the small cube would be 1/24th of the total area of the large cube; therefore, the flux through the shaded area would be
Φ=1/24𝑞𝜀